This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Variations in breast tissues resulting from the menstrual cycle are not well understood. Yet these fluctuations can compond measurements of detailed breast physiology if not properly accounted for in functional measurements. We have planned the most detailed measurements of breast tissue physiology throughout the menstrual cycle, to the best of our knowledge. Measured variations will be correlated with the expected hormonal influences that characterize menstrual cycle variations in tissues.